Delta Sigma (.DELTA.-.SIGMA.) Analog-to-Digital converters (ADCs) and digital-to-analog converters (DAC's), collectively referred to as .DELTA.-.SIGMA. data converters, are widely used in high-precision, low bandwidth applications, such as digital audio processing. Through the use of oversampling, the data path width can be reduced from, for example sixteen bits to one bit. The resultant quantization noise due to quantizing from sixteen bits to one bit is shaped such that the noise is moved outside of the signal band. The use of the smaller data path facilitates the design of the analog circuit, since a data path of, for example, one bit is the easiest for analog design.
To improve the performance of a .DELTA.-.SIGMA. data converter, noise shaping is utilized. By increasing the order of the noise shaping, this inband noise performance can be improved. The primary purpose for utilizing the one bit modulator is the inherent linearity associated therewith, since one bit only requires two levels, requiring a straight line therebetween. The reason for going to a multi-bit modulator is primarily due to the lower out of band noise, which requires less analog circuitry for the filtering thereof. Other advantages are that it a) the modulator is more stable requiring less order with a higher gain factor, b) its inband noise is smaller, and c) there is less output jitter sensitivity since the steps are smaller in the output. Linear performance can only be achieved if the steps between adjacent output levels of each DAC have very nearly the same magnitude. This, therefore, requires a matching precision that is on the order of the desired precision of the overall data converter, and this is often beyond the practical limits of present manufacturing technology.
In order to solve the problem with element matching, various techniques have been utilized such as dynamic element matching in multi-bit noise-shaping DACs. In these techniques, the mismatches are accepted as inevitable, with their negative effects being avoided through signal processing, i.e., an intelligent selection of the DACs that are utilized in the conversion.